The present invention relates to an apparatus for manufacturing a liquid crystal panel and a method thereof. More particularly, it relates to an apparatus for manufacturing a liquid crystal panel and a method thereof in which two substrates are faced to each other with spacers interposed therebetween, and while applying pressure to these substrates, adhesive arranged at peripheral portions are cured to be adhered to the substrates.
FIGS. 6 and 7 are schematic, sectional views for explaining a manufacturing method by means of a fixing apparatus for a liquid crystal panel as described in Japanese Unexamined Patent Publication No. 88018/1982. In FIGS. 6 and 7, 1 and 2 denote a pair of upper and lower substrates which are a color filter substrate and a TFT substrate having desired patterns formed thereon. Between the upper substrate 1 and the lower substrate 2, there are provided a plurality of spacers 51 of approximately 5 microns for maintaining the clearance, and the upper substrate 1 and the Lower substrate 2 are fixedly attached together at their peripheral portions via adhesive 52. This adhesive 52 finally serves as a bulkhead for enclosing liquid crystal within the substrates 1,2. 53 denotes a base (surface plate) that is made, for instance, of stainless steel, and 54 denotes a bendable material which covers at least one of the substrates. The bendable material might be a polyester film or silicone rubber sheet.
According to this conventional manufacturing method for a panel, the spacers 51 are dispersed on an inner surface of either of the upper and lower substrates 1,2 and after applying adhesive to a peripheral portion of the other substrate, both are overlapped at high positioning accuracy. Further, the whole temperature is raised while applying pressure to the substrates, the adhesive 52 is cured, and the upper and lower substrates 1,2 are fixedly attached together without generating any shifts.
At this time, the substrates are maintained in a vessel comprising at least partly of a bendable material, at least one of the substrates is covered with the bendable material, and fixing of the substrates is performed in a condition in which the interior of the vessel is decompressed or pressure is applied on the vessel from the exterior. By the above arrangements, pressure can be applied to the substrates in an uniform manner.
Such a method in which the substrates are applied with pressure by means of a material having bendable characteristics is effective in remarkably improving the uniformity of pressure application than compared to methods in which surface plates of high rigidity are employed. Consequently, irregularities or uniformities in display owing to deficiencies in gaps can be decreased.
A manufacturing method for panels employing a heating method is proposed in Japanese Unexamined Patent Publication No. 232420/1993. As shown in FIG. 8, there are respectively provided a plurality of hot plates 55 above and below substrates 1,2 in this method so that the whole panel can be heated. With this arrangement, characteristics such as rapid heating and soaking can be improved than compared to a method in which a side surface of the panel is heated employing a heater in a furnace.
However, while the manufacturing method according to FIGS. 6 and 7 is effective to some extent with respect to deficiencies in gaps, it cannot prevent shifts in lateral directions of the upper and lower substrates 1,2 or generation of wraps in the substrates. Especially in cases in which two pairs of substrates have been arranged in an aligning manner in a single vessel for the sake of improving productivity, it was found that the shift in lateral directions became larger. Further, this method presents a drawback that the substrates are apt to camber, depending on the way of heat transmission, since heating of the substrates 1,2 is performed in a furnace. That is, when heat is transmitted from downward the furnace, there is generated wrap like a bimetal, since the surface plate 53 of stainless steel is first heated, and since the thermal expansion coefficient of the surface plate 53 of stainless steel is larger than those of the substrates 1,2. If the wrap in the substrate becomes not less than a certain value, it cannot be assembled into a product and thus becomes a defective article. Especially, since requirements with respect to shapes of substrates are becoming increasingly higher accompanying requirements of thin-sizing of products in these years, this results in a drawback that the yield is further decreased. In case a gradually heating process or a method in which the rigidity is increased (the thermal capacity is increased) is employed for the sake of preventing cambers, it will not be acceptable in terms of productivity.
On the other hand, in the method of FIG. 8 in which hot plates 55 are employed, heat is transmitted from the upper and lower substrates so that occurrence of wraps is decreased; however, it cannot prevent shifts of the upper and lower substrates in lateral directions by several .mu.m, and in case request for the positioning accuracy become higher for the sake of improving the performance of liquid crystal, shifts between substrates; will not be within acceptable values. Further, it has become relevant from experiments that in the prior art arrangement, the amount of shift became larger, than compared to a case in which the substrates 1,2 are disposed in the center of the surface plate, when they were shifted from the center or when small substrates have been disposed in an aligning manner. From these results, it has become relevant from experiments that shear stress is generated between the surface plate and the substrate and between both substrates owing to differences in coefficients of thermal expansion of upper and lower surface plates or differences in friction coefficients between a surface plate and a substrate depending on the position of the substrates and the upper and lower surface plates. Power is most apt to be released especially between substrate 1 and substrate 2 that are adhered to each other only at their peripheral portions by means of soft adhesive (that is cured after heating) so that shift is generated between the substrates 1,2.
While increase of thermal capacity of the hot plates is effective for securing soaking characteristics in this conventional method, it presented a drawback that this was performed at the expense of heating/cooling speed.
Further, in surface plates made of stainless steel that are designed to be flat at a room temperature, undulations might occur in the surface plates themselves depending on the temperature distribution in the surface plates. Therefore, there was presented a drawback that wraps occurred in substrates that were fixedly attached as to be parallel thereto at a certain area of dispersion.
The present invention has been made in view of the above circumstances, and it is an object thereof to provide a manufacturing apparatus for a liquid crystal panel and a method thereof capable of decreasing amounts of overlapping shifts after fixing two substrates.